1. Field of the Invention
The invention relates to computer controlled exercise machines, and in particular, to a system for optimizing the exercise of skeletal muscles under program control.
2. History of the Prior Art
Throughout history, men have sought to improve the athletic and job oriented performance of their bodies by engaging in physical exercise to improve the size, strength, and tone of the skeletal muscles. One of the earliest ways in which such exercise was practiced, and which persists today, is the use of free weights to provide a resistance to either compression or extension of a muscle group and thereby produce growth in the size of the muscle group in response to the repeated stress placed thereon.
One difficulty with free weight exercise is that an initial amount of force is necessary to overcome the inertia of first movement of the weight and thereafter less force is required to continue movement of the weight. Thus, selecting a free weight of a size sufficient to create a desired resistance against the muscles results in most of the muscular movement being against a force substantially less than the force required to overcome the initial inertial resistance to movement of the free weight.
Another well known principal of exercise physiology is that as a skeletal muscle is exercised, it is capable of exerting varying amounts of force over its range of movement. For example, in a simple biceps exercise when a weight is lifted by bending the elbow to bring the hand holding the weight near to the shoulder (a biceps curl) the amount of force which the muscle is capable of exerting against the resistance of the weight varies over the range of movement from a position where the arm is straight to a position where the arm is near the shoulder. Further, the particular pattern of variation of muscular force varies from individual to individual. This makes it even more difficult to maintain an optimum force of resistance to muscular movement over its full range of movement.
A dramatic improvement in exercise technology was effected by the advent of "iso-kinetic" exercise machines wherein the amount of force against which the muscle is required to act is varied over the a range of movement of the muscle. Such devices frequently employ eccentric cam mechanisms which cause the resistance of the machine to movement by the user to vary in accordance with the angular position of the eccentric cam mechanism. In this manner, a muscle group being exercised is opposed by a lower force of resistance in the region of its movement where less force is available from the muscle and by a greater force of resistance in regions of movement where the muscle has greater strength. These mechanisms greatly improve the rate at which muscular development may be effected. Such devices, however, include an inherent limitation in that the pattern of muscular strength variation over range of movement varies from individual to individual and a standard eccentric cam pattern can not optimize the resistance variations necessary for different individuals. In addition, when the exercise mechanisms are used in a rehabilitation or therapeutic environment, the muscular strength pattern of an individual may vary even more dramatically from that of a standard pattern and in some regions of movement virtually no strength exists at all and it would be desirable to provide positive assistance to the movement of the muscle rather than even the lowest degree of resistance. Iso-kinetic machines are totally incapable of applying such positive movement assisting forces.
Further improvement in the technology of exercise occurred with the advent of systems which monitor the amount of force which is exerted by a user and employ a feedback loop to provide a proportional amount of resisting force to custom configure the resistant force to the individual and to the actual muscular strength available at each point over a given range of movement. Such systems have conventionally employed either hydraulic or pneumatic means to oppose the force applied by the muscle and a transducer to measure the quantity of force being applied and generate an analog signal. The analog signal is converted to a digital signal and then compared to the value of the desired force stored in memory. If an error exist then the comparison device generates a control signal which commands a servo-motor to change the force controlling device until no error signal exists. Major problems with such systems are that their response time is very slow since the servo-motor must physically move in a very precise manner and that the electromechanical interface must include very tight mechanical tolerances in order to achieve the required accuracy. The difficulty of achieving these tolerances results in instability and oscillation. Such systems are shown in U.S. Pat. Nos. 4,235,437 to Ruis et al; U.S. Pat. No. 4,227,689 to Keiser; and U.S. Pat. No. 4,354,676 to Ariel.
A disadvantage inherent in the very nature of feedback loop controlled exercise systems is that it is extremely difficult to provide a transitional interface between the hydraulic or pneumatic force applying mechanisms and the electrical transducer mechanisms forming a critical part of the feedback loop. As a result, such systems are extremely unstable, prone to oscillation, and do not reliably perform the function intended. Other systems, such as that shown in U.S. Pat. No. 3,869,121 to Flavell have proposed to utilize a servo-system to control the electrodynamic braking force generated by an electric motor for providing a varying force of resistance as a bar is lifted and which is then used as a motor to provide a varying force of resistance as the bar is lowered. Feedback control is used to maintain a constant velocity by varying the force of resistance. Such systems are incapable of programming a velocity variation between the upper and lower limits of movement and, further, incorporate all of the instability problems inherent in classical servo-loop controlled systems.
Certain other relatively elaborate feedback controlled exercise systems have been disclosed in the prior art in which an electronic controlled device varies the forces in accordance with the prestored program and in some cases may alter the force characteristics in relation to the performance achieved by the individual performing the exercise. Additionally, some devices may even use a microprocessor to record the performance, alter the forces in a preprogrammed manner and provide a display indicating the progress of the individual both over a period of time and on an instant basis as the exercise is being performed.
The exercise system of the present invention does not include a transducer/feedback loop but rather employs a current controlled DC motor to vary the force of resistance to muscular movement. Current mode switching technology is employed to very accurately control the motor torque using only electrical signals which thereby increases the response time of the system by several orders of magnitude over the prior art electrically and mechanically interfaced feedback systems.
A permanent magnet DC motor operated in the current control mode is used to vary the force of resistance throughout the range of movement under direct programmed control by a computer. The very precise control over the variable resistance against muscular movement available with this technique enables the provision of resisting forces custom-taylored to individual requirements.
The present system allows not only an increase in the rate of improvement in muscle strength and joint flexibility but also the teaching of the user to achieve preselected optimum patterns of movement routines including speed, force, and rates of variation therein. With variable resistance exercise systems, whether of the prior art variable cam or feedback loop variety or that of the present invention, the technique of movement used is as important to the training effort as the exercise forces. The natural inclination is to lift and move as much weight as possible, with technique being secondary. Very strong training discipline is needed to overcome this natural human tendency. With the system of the present invention, proper exercise technique is insured by the computer, so that training goals and rates of improvement in performance are greatly accelerated.
The monitoring and control techniques of the system of the present invention allow multi-axis monitoring of complex joint movement to be provided so that it is unnecessary to restrain movement except about only one axis in order to effect measurement or therapy. Variable resistance exercise may be programmed in all three dimensions, the way certain limbs move naturally. In addition, specialized multi-axis training programs are also possible. For example, a golfer who wishes to improve his swing can select a program which forces him to use the proper muscles in the correct sequence and also provides a totally objective measurement of his performance. Application of the present system to any sport or other physical activity is possible by modification of the software controls.
In the therapeutic and rehabilitative fields of exercise physiology, the system of the present invention allows accurate measurement of very limited strength and the precise location of joint movement anomalies. The assistive and resistive abilities of the present system gives rehabilitative technologists exact information about the state of muscle deterioration and/or regeneration to a degree not heretofore available.